This invention relates in general to wireless communication systems, and more specifically to a method and apparatus for providing a distributed architecture digital wireless communication system.
Current CDMA systems implement soft handoff, where a mobile station (MS) communicates with multiple base transceiver stations (BTS) simultaneously during a transition from one cell to another. However, since multiple BTSs transmit to a single MS, soft handoff, in many real-world cases of interest, either wastes system capacity or creates additional interference on the forward link. Fast cell site selection (FCSS) eliminates the soft handoff by switching the forward link from the first BTS to the second BTS very quickly such that only one BTS transmits to a MS at any given point in time.
The challenge with FCSS is that the packet data for the MS queued at the first BTS must be available at the second BTS so that the packet data flow to the MS is seamless. Any delay in continuing the packet flow may result in a loss of system capacity or throughput, and the repetition of packets will result in a loss of system capacity and increased interference. The key to the success of FCSS is therefore to make the packets directed from the network to the MS available at both BTSs, and to keep the packet queues synchronized such that the FCSS is as seamless as possible.
Prior art systems have used a centralized architecture in which the scheduling of data packets and the Automatic Repeat reQuest (ARQ) function have been performed in a central controller. This centralized architecture imposes more delay than is desirable for FCSS (or any scheme using soft handoff). Thus, what is needed is a new architecture for a digital wireless communication system that will reduce the scheduling and ARQ delays observed in the prior art centralized systems.